One of the factors or problems encountered in electrostatic printing or xerography in office copiers and printers in which the image is fused on the paper under heat and pressure is that the process tends to cause a curl to be formed in the paper. Curled paper is difficult to handle in a receiver for the sheets. Ideally the sets should be neat with edges aligned and easy to handle by an operator or in finishing apparatus in which the set may be stitched or stapled.
The curl problems with sheets of paper stem from the treatment of the sheets in the processor. A sheet of normal paper is taken from a supply cassette or feeder, in an environment in which the paper is subject to humidity and absorbs a certain amount of moisture. The sheet is processed past a photo conductor where powder or liquid ink is applied to produce an image, and then the sheet is passed through a fuser and subjected to heat and pressure between rollers, with the result that normal, flat sheets are caused to curl. Curled sheets received in a collator or sorter in bins cause failure of the device due to jamming or mis-sorting of sheets and the bin capacity of the receiver is reduced. In addition, curled sheets do not tend to form neat stacks or sets.
In efforts to minimize curl problems in copiers and printers, the feed rolls may be modified or bins made larger, but there has been prior to the present invention, no way to remove the curl from paper sheets by returning it to its original, normal flat condition, without requiring the use of complex positively driven rolls with large power consumption and tracking or sheet receiving problems resulting from the use of pressure plates and the like, wrinkling of sheets or smearing of print.